PROBES/ /2008
DEVELOPMENT OF NATIONAL EMISSION STANDARDS FOR
PETROCHEMICAL PLANTS
CENTRAL POLLUTION CONTROL BOARD
(Ministry of Environment & Forests, Govt. of India) Parivesh Bhawan, East Arjun Nagar
Delhi – 110 032 September 2008
Project Team
1. Sh. P.M. Ansari, Additional Director - Report Finalisation
2. Dr. D.D. Basu, Senior Scientist - Co-ordination, supervision &
Preparation of report 3. Sh. Paritosh Kumar, Sr. Env. Engineer - Report processing
4. Sh. Dinabandhu Gouda, Env. Engineer - Data compilation, analysis and
Preparation of report
5. Sh. Atul Sharma, JLA - Secretarial assistance 6. M/s. Aditya Environmental Service, - Project execution
Mumbai
7. M/s. Lurgi India Private Limited - Project execution New Delhi
CONTENTS
S. No. Items Page No.
List of Contents i
List of Figures vi
List of Tables vii
List of Annexure viii
List of Acronyms ix
1.0 Introduction 1
1.1 Introduction 1
1.2 Classification 1
1.3 Approach for development of emission standards 4
1.4 Methodology 4
2.0 Status of Petrochemical Industry in India 7 2.1 Usage Pattern of Basic Intermediates 10
2.1.1 Ethylene 10
2.1.2 Propylene 10
2.1.3 C4 Fractions – Butylenes / Butadienes 11
2.1.4 Benzene 12
2.1.5 Toluene 13
2.1.6 Xylene 14
2.2 Feed Stock choice 14
2.3 Downstream Petrochemicals 15
2.3.1 Products based on Ethylene 15 2.3.1.1 Ethylene Oxide and Ethylene Glycol 15 2.3.1.2 Ethylene Dichloride / Vinyl Chloride 16
2.3.1.3 Ethyl Benzene / Styrene 16
2.3.2 Propylene based petrochemicals 17 2.3.2.1 Propylene oxide and Propylene Glycol 17
2.3.2.2 Acrylonitrile 17
2.3.2.3 Isopropyl alcohol 17
2.3.2.4 Cumene 17
2.3.2.5 Phenol / Acetone 17
2.3.2.6 Butanol and 2-Ethyl Hexanol 18 2.3.3 Petrochemicals from Benzene 18 2.3.3.1 Cyclohexane and Caprolactum 18
2.3.3.2 Maleic Anhydride 18
2.3.4 Petrochemicals from Toluene 18
2.3.4.1 Toluene diisocyanate 18
2.3.5 Chemicals from Xylene 19
2.3.5.1 Terephthalic acid and Dimethyl
Terephthalate 19
2.3.5.2 Phthalic Anhydride 19
2.4 Observations and Findings – Industry survey 19
3.0 Manufacturing Process 21
3.0 Unit Process 21
3.1 Ethylene / Propylene 22
3.2 Butadiene 25
S. No. Items Page No.
3.3 Ethylene Oxide 27
3.4 Ethylene Glycol 30
3.5 EDC & VCM 32
3.6 Propylene Oxide / Propylene Glycol 35
3.7 Isopropyl Alcohol 36
3.8 Acrylonitrile 36
3.9 Benzene and Toluene 39
3.9.1 Manufacture of Benzene and Toluene from pyrolysis
gasoline 39
3.9.2 Toluene dealkylation and Toluene disproportionation
process 44
3.10 Xylene 48
3.10.1 Xylene manufacture by Naphtha reforming 48 3.10.2 Xylene production from pyrolysis gasoline 54
3.11 Maleic Anhydride 54
3.12 Phenol / Acetone / Cumene 55
3.12.1 Cumene from Benzene and Propylene 55 3.12.2 Phenol from Cumene by peroxidation 55
3.13 Toluene Diisocyanate 57
3.14 Phthalic Anhydride 59
3.15 Dimethyl Terephthalate 61
4.0 Emission Sources in Petrochemical Plants 64
4.0 Common emission sources 64
4.1 Emission from combustion sources (power and steam generation) 64 4.2 Emission profile from olefin complex 65 4.2.1 Plant boundary definition and the degree of
integration 65
4.2.2 Emission related to feed stock 67
4.2.3 Scale of operations 67
4.2.4 Plant age 68
4.2.5 Air emission / emission factors and inventory 68 4.3 Emission from cracker furnace (steady state operation) 68 4.3.1 Emission from cracker furnace (de-coke operation) 70 4.3.2 VOC from cracking process 71 4.3.3 Emission inventory from olefin complex 72
4.4 Emission from aromatic plants 72
4.4.1 Volatile organic compounds from aromatic plants 73
4.5 Emission from butadiene plants 74
4.5.1 Process vent 75
4.5.2 Fugitive emissions 75
4.6 Emission from xylene plants 76
4.7 Emission from ethylene oxide and ethylene glycol plant 77 4.8 Emission from EDC and VCM plants 80
4.9 Emission from acrylonitrile 83
4.10 Emission from phathalic anhydride 87 4.11 Emission dimethyl terephthalate 88 4.12 Emission due to transfer operations 88
S. No. Items Page No.
4.12.1 Emission during tanker loading 89
4.13 Storage emission 91
4.13.1 Storage emission from ethylene and propylene plant 91 4.13.2 Storage emission from butadiene 92 4.13.3 Storage emission from benzene plants 92 4.13.3.1 Monitoring of emission from benzene
storage tanks 93
4.13.4 Storage emission from EO 94 4.13.5 Storage emission from EDC 94 4.13.6 Storage emission from ACN 95 4.13.7 Storage emission from xylene 96 4.13.8 Storage emission from DMT 96 4.13.9 Fixed roof storage vessel 96 4.13.10 Floating roof storage vessel 97 4.13.10.1 External floating roof (EFR) vessel 97 4.13.10.2 Internal floating roof (IFR) vessel 98 4.13.10.3 Emission from floating rook tanks 98
4.14 Flares 99
4.14.1 Flare from cracker furnace 99
4.15 Fugitive emission 100
4.15.1 Estimating fugitive emission 103 5.0 Categorisation of Volatile Organic Compounds (VOCs) 107
5.1 VOC Emission from Petrochemical / Synthetic Organic Chemical Manufacturing Industries / Polymer Processes 107
5.2 Categorisation of VOCs 107
5.3 Overview of Environmental Impact of VOCs 114 5.3.1 Adverse physiological effects 114
5.3.2 Damage to materials 115
5.3.3 Photochemical oxidant production 115 5.3.4 Stratospheric ozone depletion 115
5.3.5 Global warming 115
5.3.6 Odour 116
5.4 Criteria adopted for Categorisation of VOCs 116 5.5 VOC Impact Data used in the Project 116 5.5.1 Adverse physiological effects 117
5.5.2 Damage to materials 117
5.5.3 Photochemical oxidant production 117 5.5.4 Stratospheric ozone depletion 119
5.5.5 Global warming 119
5.5.6 Odour 120
5.6 Categorisation Method of VOCs 121
5.7 Findings in the Study 123
5.8 Reference 123
6.0 Emission Control Technologies in Petrochemical Industries 127
6.1 Combustion Control Devices 127
6.1.1 Thermal incinerators 128
6.1.2 Catalytic incinerators 128
S. No. Items Page No.
6.1.3 Industrial boilers and process heaters 128
6.1.4 Flares 128
6.1.5 Halogenated streams 129
6.2 Product Recovery and Recapture Devices 129
6.2.1 Condensers 129
6.2.2 Adsorption 130
6.2.3 Absorption 130
6.3 Control Techniques specific to Transfer Operations 131 6.3.1 Vapour collection system 132
6.3.2 Vapour balancing 132
6.3.3 Route to a process for fuel gas system 132 6.4 Control Techniques Specific to Storage Vessel 132
6.4.1 Fixed roof vessel 132
6.4.2 Floating roof vessels 132
6.4.3 Route to a process or a fuel gas system 133
6.5 Best Available Technology 133
6.5.1 Best available technique for air pollution reduction in
cracker furnace 133
6.5.1.1 Emission control technology for existing cracker units in India 138 6.5.2 Best available techniques for air pollution reduction
for EO / EG 139
6.5.2.1 Emission control priorities for existing
plants of EO/EG 142
6.5.3 Best available techniques for air pollution reduction
for EDC and VCM 142
6.5.4 Best available techniques for air pollution reduction
for ACN 147
6.5.4.1 Emission control priorities for existing
plants 149
6.5.5 Best available techniques for air pollution reduction
for benzene and toluene 149
6.5.6 Best available techniques for air pollution reduction
of xylene 152
6.5.7 Emission control priorities for existing units in India 152 7.0 Proposed Emission Standards and LDAR Guidelines
7.0 Introduction 162
7.1 Air Pollutant and Risk Associated with them 162 7.2 Source of Pollutants in Petrochemical Plants considered for
Development of Standards 163
7.2.1 Volatile organic compounds (VOCs) emission sources 164 7.3 Approach to Emission Regulation 166
7.3.1 Conventional parameters 166
7.3.2 Inorganic pollutants 166
7.3.3 VOC control 166
7.4 Present Status of Emission Control 167 7.5 Proposed National Emission Standards 167
S. No. Items Page No.
7.5.1 Emission standards for heater / furnace / boiler /
vaporiser 168
7.5.2 Emission standards for organic particulates 168 7.5.3 Emission standards for process emission (specific
organic pollutants) 168
7.5.4 Emission standards for VOC – HAPS from process
vents 169
7.5.5 Emission standards for VOCs (general) from process
vents 169
7.5.6 Standards for storage and transfer point (loading and
unloading) 169
7.5.6.1 Standards for atmospheric storage tanks of petrochemical products 169 7.5.6.2 Storage of benzene, VCM and ACN 170 7.5.7 Standards for emission from loading of volatile
products 170
7.6 LDAR Guidelines 171
7.6.1 Guidelines for atmospheric storage tanks practices 171 7.6.2 LDAR and monitoring protocol 171
7.6.3 General notes 173
Bibliography 175
LISTOFFIGURES
S. No. Figure Page
No.
1.1 Petrochemical product tree 5
1.2 Methodology adopted for the Study 6 2.0 State-wise production in the year 2004-05 9 2.1.1 Sectoral usage pattern: ethylene 10 2.1.2 Sectoral usage pattern: propylene 11
2.1.3 Sector usage: butadiene 12
2.1.4 Sectoral usage pattern: benzene 13 2.1.5 Sectoral usage pattern: toluene 14 3.1 Block diagram – olefin manufacture 23 3.2 Simplified flow diagram – butadiene manufacture 45
3.3 Block diagram- EO manufacture 46
3.4 Block diagram – glycol manufacture 47 3.5 Block diagram – EDC / VCM manufacture (balance process) 48 3.6 Block diagram – acrylonitrile manufacture 49 3.7 Benzene / toluene extraction from pyrolysis gasoline (using liquid
– liquid extraction) 50
3.8 Process flow diagram for hydro-treating 51 3.9 Benzene / toluene extraction for pygas using extractive
distillation 52
3.10 Process flow diagram of a toluene dealkylation unit (HDA) 53 3.11 Toluene diproportionation process flow diagram (tatoray
process) 54
3.12 Block diagram of xylene process (IPCL, Vadodara) 55 3.13 Process flow diagram for hydro-treating 56 3.14 Process flow diagram for reformer unit 57 3.15 Block diagram for maleic anhydride 58 3.16 Block diagram for phenol / acetone 59
3.17 Block diagram for TDI 60
3.18 Block diagram for phthalic anhydride 62 3.19 Manufacturing process and block diagram of DMT 63 5.1 Decision tree for categorisation of volatile organic compounds 126 6.1 Discrete burner, thermal incinerator 153
6.2 Catalytical incinerator 154
6.3 Steam – assisted elevated flare system 155 6.4 Schematic diagram of a shell and tube surface condenser 156 6.5 Two stage regenerative adsorption system 157 6.6 Packed tower absorption process 158 6.7 Tank truck loading with vapour recovery 159
6.8 Dual arm loading rack 160
6.9 Vapour balancing system 161
LIST OF TABLES S.
No. Table Page
No.
1.1 Classification of petrochemical products 3 2.1 Industries with various feedstocks 7 2.2 Production and installed capacities for major intermediates in
India 9
2.1.2 Propylene: usage ratios 11
2.1.3 Butadiene: usage ratios 12
2.1.4 Benzene: usage ratios 13
2.2.1 Plant-wise feedstock requirement 15 2.3.1.1 Ethylene oxide / ethylene glycol: installed capacities 16 2.3.1.2 Installed capacity: EDC / VCM 16 2.3.5.2 Phathalic anhydride (PA): capacity / production data 19
4.1 Cracker – flue gas analysis 70
4.2 Olefin complex (0.5 MMTPA ethylene): typical emission
inventory 72
4.3 Emission sources and pollutants from various aromatic plants 73 4.4 Combustion emission to air from aromatics processes (in kgt/t
feedstock) 73
4.5 Fugitive emissions – butadiene 75
4.6 Work place monitoring data 75
4.7 Monitoring of flue gases (Unit – V) 77 4.8 Process vent analysis (EO/EG) 78 4.9 Fugitive emissions calculations 79 4.10 Process vent analysis results – EDC / VCM 80 4.11 Analysis of incineration off-gases 81 4.12 Fugitive emission control practices – existing units 82 4.13 Estimation of fugitive emissions from a typical plant (Unit – I) 83 4.14 Acrylonitrile plant process vents (Unit-I) 84 4.15 Acrylonitrile plant stack emissions (Unit-I) 86 4.16 Fugitive emission prevention – acrylonitrile (Unit – I) 86 4.17 Component fugitive emission – acrylonitrile (Unit – I) 87 4.18 Analysis results – phthalic anhydride absorber vent (Unit – VI) 88 4.19 Analysis results – adsorber off-gas analaysis (Unit – VII) 88 4.20 Tanker loading practices – benzene 89 4.21 Work area benzene monitoring levels near tanker loading bay
(situation: no vapour collection / control device provide) (Unit – V)
90
4.22 Monitoring at tanker lading bay emission control system (Unit
– V) 90
4.23 Storage practices for liquid hydrocarbons 91 4.24 Storage practices for benzene 92 4.25 Monitoring of emission during tank filling 93 4.26 Monitoring of emission during tank breathing 93 4.27 Storage emission – EO / EG plant 94
S.
No. Table Page
No.
4.28 Storage emission – EDC plant (Unit – I) 95 4.29 Storage emission ACN plant (Unit – I) 96 4.30 Comparison of elevated flares in petrochemical units 100 4.31 Leaking indices for a centrifugal pump with different types of
seals 102
4.32 Average emission factors for fugitive emissions 104 4.33 Leaking and non-leaking emission factors for fugitive
emissions (kg/hr source) 105
4.34 Stratified emission factors for equipment leaks (kg / hr
source) 106
5.1 VOC emissions in petrochemical / synthetic organic chemical
manufacturing industry (SOCMI)/polymer process 108 5.2 Categorisation of volatile organic compounds (VOCs) 124 6.1 Maximum emission levels in treated off-gas 159 7.1 Emission of inorganic pollutants from petrochemical plants 170 7.2 Volatile organic compounds emission from point and non-
point source 171
LISTOFANNEXURE
No. S. Annexure Page
No.
I References List 184
LIST OF ACRONYMS ABS - Alkyl Benzene Sulphonate
AF - Acrylic Fibre
BAT - Best Available Technology
BPCL - Bharat Petroleum Corporation Limited
BRPL - Bongaigaon Refineries & Petrochemical Limited CAA - Cuprous Ammonium Acetate
CRL - Cochin Refinery Limited DEA - Di-ethanol amine DMF - Di-methyl Formamide DMT - Dimethyl Terephalate DVH - Dry-vent Header
EB - Ethyle Benzene
EDC - Ethylene Dichloride EFR - External Floating Route
EG - Ethylene Glycols
EO - Ethylene Oxide;
GAIL - Gas Authority of India Limited GWP - Global Warming Potential HAD - Hot Alkali Digester
HCN - Hydrogen Cyanide HDA - Hydrodealkylation HDPE - High density polyethylene
HOCL - Hindustan Organic Chemical Limited HPCL - Hindustan Petroleum Corporation Limited HPL - Haldia Petrochemical Limited
IARC - International Agency for Research in Cancer IFR - Internal Floating Route
IOC - Indian Oil Corporation IPA - Isopropyl alcohol
IPCL-MGCC - Indian Petrochemical Corporation Limited – Maharashtra Gas Cracker Complex
ISBL - Inside Battery Limit
LDAR - Leak Detection And Reaper LDPE - Low density polyethylene LNB - Low Nox Burner LPG - Liquefied Petroleum Gas MA - Maleic anhydride
MDI - Methylene Diphenyl Di-isocyanate MMTPA - Million Metric Tonne Per Annum MNT - Mono-nitro Toluene MRL - Mangalore Refinery Limited MTD - Meta Toluene Diamine
NEP - National Environmental Policy NFY - Nylon filament Yarn
NGL - Natural Gas Liquid
NMP - N-methyl Pyrolidone
NOCIL-TTC - National Organic Chemical Industries Limited – Trans Thane Creek
OA - Oswal Agro
ODCB - Ortho Dichloro Benzene ODP - Ozone Depleting Potential OSBAL - Outside Battery Limit
PA - Phthalic anhydride PAREX - p-Xylene
PBR - Poly Butadiene Rubber PFY - Polyster Filament yarn
PG - Proplene Glycol
PGH - Pyrolysis Gasoline Hydrogenation
PO - Propylene Oxides
POCP - Photochemical Ozone Create Potential PR - Polyurathene Resins
PRV - Pressure Relief Valve PSF - Polyster staple fibre PTA - Terephthalic acid PVC - Poly Vinyl Chloride RIL - Reliance India Limited RINL - Rashtriay Ispat Nigam Limited SAIL - Steel Authority of India
SBR - Styrene Butadiene Rubber SF - Synthetic Fibre
SOCMI - Synthetic Organic Chemical Manufacturing Industry SRV - Safety Relief Valve
TDI - Toluene Di-Isocyanate TLV - Threshold Limit Value TPA - Tonne Per Annum TPM - Total Particulate Matter TVP - True Vappor Pressure TWA - Time Waited Average ULNB - Ultra Low Nox Burner VCM - Vinyl Chloride Monomer
VOC - Volatile Organic Compound WVH - Wet vent Header
MEG - Mono Ethylene Glycol
CHAPTER-1 INTRODUCTION 1.1 Introduction
Petrochemicals are hydrocarbons, obtained from naturally occurring raw materials viz. petroleum, natural gas, coal etc. Coal was initially the basic raw material for organic chemical industry. However the basic feedstock has changed recently from coal to petroleum. This is attributed to the recent innovation and technological advance in the field of chemical industry based on petroleum feedstock. The handling and processing cost of petroleum based raw materials to down-stream products are cheaper than that of based on coal even though the cost of coal is cheaper than the petroleum based feedstock. The emergence of downstream petrochemical products manufacturing industries (popularly called synthetic organic chemicals manufacturing industries) like high polymers, synthetic fibres, plastic and plasticizers, synthetic rubbers, pesticides, carbon black, detergents, fertilisers and other similar products are outcome of the technological developments in the field of chemicals based on petroleum feedstock. These feedstock’s can either be cracked (in cracker complexes) to produce olefins or reformed (in aromatic complexes) to produce aromatics.
These olefins and aromatics are grouped together as basic petrochemicals and form the major building blocks.
Synthetic organic chemicals can also be obtained from other alternative sources like ethyl alcohol from molasses or acetylene from calcium carbide or benzene from coke oven by products. But through the application of new process technology in the field of petrochemicals based on feedstock available from refineries, there is a positive shift to petroleum feedstock. The raw materials of petroleum origin are crude oil, natural gas, off gases residues from refinery. In general, the manufacturing process of petrochemicals involves raw materials undergoing one or more chemical reactions followed by different unit operations to separate the product from side products and co-products.
The ranges of chemicals in systematic sequential chain produced in petrochemical industries are presented in Fig. 1.1.
1.2 Classification
The entire product spectrum can be classified into the following three classes:
 Building block or primary petrochemical products
 Intermediate products or secondary petrochemical products, produced from building block
 Final or end products, coming from intermediate products.
The chemicals falling under the three classes are listed in Table 1.1. Each class is further classified based on nature of products.
Table 1.1: Classification of Petrochemicals products Feedstock Primary
products Intermediate products Final Products Naphtha Olefins/Diolefins
1.Ethylene 2. Propylene 3. Butadiene Aromatics 1. Benzene 2. Toluene 3. Xylene
Organics
1. Ethylene Oxide 2. Ethylene Glycols 3. Propylene Oxides 4. Isopropyl alcohol 5. Acetone
6. 2-Ethyl alcohol 7. Phthalic
anhydride(PA)
8. Maleic anhydride(MA) 9. Phenol
10. Styrene 11. Polyethylene 12. Chlorinated
hydrocarbon 13. Isocynates 14. Cumene 15. Butanol Synthetic fibre
1. Caprolactum 2. Dimethyl
Terephalate(DMT)/
Terephthalic acid(TPA) 3. Acrylonitrile
Plastics and resins
1. High density
polyethylene (HDPE)/
Low density polyethylene (LDPE)
2. Polypropylene
3. Poly Vinyl Chloride (PVC)
4. Polystyrene 5. Alkyl Resins
6. Polyurathene Resins 7. Resins PF
8. Alkyl Benzene
Sulphonate (ABS) Resins
Synthetic Fibre:
1. Nylon filament Fibre 2. Nylon tyre cord and
other fibre
3. Polyster Filament yarn 4. Polyster staple fibre 5. Acrylic Fibre
6. Polypropylene fibre Synthetic Rubber:
1. Styrene Butadiene rubber
2. Poly Butadiene Rubber
1.3 Approach for development of emission standards
Petrochemical industries manufacture various products and comprises of multiple processing units at one specific location adopting different technologies, equipments, unit process and unit operation from a basic feed stocks. It leads to generate wide spectrum of emission of air pollutants, mainly of volatile organic compounds (VOC’s). Some of them are toxics, carcinogenic. Some are responsible for damage to materials. Some of them have potential to photochemical oxidant creation, global warming, ozone depleting and creation of malodour. Besides these various types of VOC’s, there are generations of various types of inorganic hazardous air pollutants. In addition to above, the generation of conventional air pollutants are there.
In order to reduce the air emission to an acceptable level, it is necessary to adopt a comprehensive approach considering, thermal destruction, good engineering practices and possible end of pipe technology with due regard to techno-economic feasibility within the frame work of National Environmental Policy (NEP), 2006. The salient feature of NEP with respect to standard, are as follows:
• Risk reduction related to health, ecosystem and manmade assets.
• General availability of required technology and techno-economic feasibility.
• Achievement of the ambient air quality standard for the location concerned.
• Quality as well as quantity of pollutants emitted.
With this backdrop, the Central Pollution Control Board had taken up a study to develop national emission standard for petrochemical manufacturing units -basic and intermediate product as outlined in Fig. 1.1.
1.4 Methodology
The basic steps to develop the emission characterisation and assessment of petrochemical are as follows:
(i) Compiling reliable emission inventory depending on type of feed stock / products and the process technology generally adopted.
(ii) Implementing the optimum strategy to minimise the emission reduction at the source and recovery at the source.
(iii) Review of data and strategies to mitigate process emission to attain goal.
(iv) Adaptation of proper & proven end of pipe (EOP) technologies for disposal / destruction (viz. flaring / incineration etc.)
The study was divided into three phases as under:
(i) Literature studies (ii) Industrial survey
• Assessment of air pollutants, categorisation of VOC ‘s and short- listing of chemicals for further study
• Review of international standards
(iii) Detailed case studies on selected petrochemicals
The detailed Methodology (phase wise) adopted for the study is presented in Fig.
1.2.
Fig. 1.1 : Petrochemical Product Tree
Olefins
Aromatics
P V C Ethylene
Butadiene
Benzene Propylene
EDC/PVC
EO/EG Isopropyl Alcohol /
Acetone Propylene oxide
Polyether
Acrylonitrile 2 Ethyl Hexanol
Cumene/ Phenol
Cyclo hexane /Caprolactum Ethyl benzene/
Styrene Detergents alkylate
Maleic anhydride
Polyethylene (LD/HD)
Polyurethane Resins Polypropylene
Plasticisers
Thermo set resins
Polystyrene
Nylon
Glycol ethers Enthaloamines Dye stuff and
chemical Intermediates
Phthalic anhydride
Pharmaceuticals Acrylic Fiber
Detergent
Alkyl Resins Polyester A B S Plastic
PBR S B R Area of coverage for emission
standard BUILDING
BLOCK
INTERMEDIATES
Primary polymer resins and
plasticisers FIBER CHEMICALS
Naptha
Assessment of regulatory practices abroad
Case studies on short listed petrochemicals to study process / fugitive emissions and flaring practices
Short-listing of chemicals for further study
Ranking of chemicals into high / medium / low categories
Assessment of eco- toxicological / environmental properties of VOC’s emitted
Data assimilation & desk study (Comprehensive listing of petrochemicals manufactured &
VOC’s emitted)
Industry survey on petrochemicals manufacture in India
Discussion with Government
Departments / Ministry etc. Discussion with
experts Discussion with Industry / Trade Association
Proposed framework for standard
Preliminary information collection and collation
Literature survey
Fig. 1.2: Methodology adopted for the study
CHAPTER- 2
2.0 STATUS OF PETROCHEMICAL INDUSTRY IN INDIA
Petrochemical industry in India is growing steadily. The locations of petrochemical units are given in Table 2.1 along with feedstock. It is observed from Table 2.1 that the major feedstock in Indian petrochemical units is naphtha and natural gas. It is also indicated that from feedstock of natural gas, olefins compounds are produced. In refinery, generally aromatic compounds are produced. The major intermediate products produced in the country are ethylene, propylene, butadiene, benzene, toluene and xylene. Of course, petrochemical products are produced throughout countries as indicated in Table 2.1. However, the major petrochemical complexes are located in the State of Maharashtra and Gujarat. The first naphtha cracker unit (Olefins) M/s United Carbide India Limited (UCIL) went into production in Mumbai at the end of 1960.
M/s National Organic Chemical Industry Limited (NOCIL), Thane near Mumbai went into production in the year 1966. The third petrochemical complex i.e. M/s Indian Petrochemical Limited (IPCL), Vadodara, using naphtha with facilities of production of primary, intermediate and downstream petrochemical products started during 1978-79. M/s IPCL commissioned their gas-cracking unit in 1989 at Nagothane in Maharashtra. M/s Reliance India Limited (RIL) commissioned their plant in 1997 at Hazira, Gujarat. In the year 1999-2000 three petrochemical complexes came into existence, these are M/s Haldia Petrochemical, West Bengal, M/s Gas Authority of India Limited (GAIL), Auriya, Uttar Pradesh, M/s IPCL, Gandhar in Gujarat.
Table 2.1: Industries with various feedstock
S. No. Name of Industry Feedstock
1 Bongaigaon Refineries, Assam Naphtha 2 Bharat Petroleum Corporation Limited, Mumbai,
Maharashtra Naphtha
3 Cochin Refinery Limited, Ernakulam, Kerala Naphtha 4 Gas Authority of India Limited, Auriya, Uttar
Pradesh Natural gas
5 Hindustan Organic Chemical Limited, Cochin,
Kerala Gas
6 Hindustan Petroleum Corporation Limited, Vizag,
Andhra Pradesh Gas
7 Haldia Petrochemical Limited, Haldia, West
Bengal Naphtha
8 Indian Oil Corporation, Mathura, Uttar Pradesh Gas 9 Indian Oil Corporation, Koyali, Vadodara,
Gujarat Naphtha
S. No. Name of Industry Feedstock 10 Indian Petrochemical Corporation Limited,
Vadodara, Gujarat Naphtha
11 Indian Petrochemical Corporation Limited,
Gandhar, Gujarat Natural gas
12 Indian Petrochemical Corporation Limited,
Nagothane, Maharastra Natural gas
13 Mangalore Refinery Limited, Mangalore,
Karnataka Gas
14 National Organic Chemical Industries Limited,
Thane, Maharashtra Naphtha
15 Oswal Agro, Mumbai, Maharashtra Naphtha
16 Reliance India Limited, Hazira, Gujarat Naphtha / Natural gas
17 Reliance India Limited, Jamnagar, Gujarat Gas 18 Reliance India Limited, Patalganga, Maharashtra Naphtha 19 Rashtriya Ispat Nigam Limited, Vizag, Andhra
Pradesh Naphtha
20 Steel Authority of India Limited, Bhilai,
Chhattisgarh Coke oven gas
21 Steel Authority of India Limited, Bokaro,
Jharkhand Coke oven gas
22 Steel Authority of India Limited, Durgapur, West
Bengal Coke oven gas
23 Steel Authority of India Limited, Rourkela,
Orissa Coke oven gas
The State-wise production in the year 2004-05 is given below Gujarat - 59%
Maharastra - 17%
West Bengal - 12%
Uttar Pradesh- 04%
Tamil Nadu - 03%
Other - 05%
Maharashtra 17%
Gujarat 59%
West Bengal 12%
Tamil Nadu 3%
Rest of India 5%
Uttar Pradesh 4%
Gujarat Maharashtra West Bengal Uttar Pradesh Tamil Nadu Rest of India
Fig 2.0: State wise production in the year 2004-05
With installation of so much units, the installed capacities of major intermediate products such as ethylene, propylene, butadiene, benzene, toluene and xylene has increased, which are summarised in Table 2.2.
Table 2.2: Production and Installed capacities of major intermediates in India Ethylene (TPA) Propylene (TPA) Butadine (TPA) Production Installed Production Installed Production Installed Total in
1997-98 1181400 2497000 580204 1559600 31000 121600 Total in
2004-05 2645000 2513000 1892000 1549000 131000 141000 Benzene (TPA) Toluene (TPA) Xylene (TPA)
Production Installed Production Installed Production Installed Total in
1997-98 357057 836220 87587 176335 220380 1835000
Total in
2004-05 640000 741000 177000 280000 146000 229000
Source: Annual report of 2005-06, Department of Chemical and fertiliser, Government of India
2.1 Usage pattern of basic intermediates 2.1.1 Ethylene
Ethylene is the basic petrochemical. All cracker complexes are designed with fixed ethylene capacity and other capacities are decided upon the basis of ethylene production. Ethylene is the basic building block of polyethylene (PE), polyvinyl chloride (PVC) and ethylene glycol. Ethylene is a prime raw material for downstream petrochemicals. Usage ratio of ethylene in the manufacture of various downstream petrochemicals is given below:
Product Ethylene required per unit
LDPE/ LLDPE 1.03
HDPE 1.04
PVC 0.54
EO 0.80
MEG 0.62
STYRENE 0.33
AO 1.03
It is observed from the ratio that polyethylene like LDPE / LLDPE, HDPE are the major ethylene based down streams products. End use pattern for ethylene according to sector of usage is presented in Fig. 2.1.1.
HDPE 34%
PVC 18%
MEG 12%
OTHERS
7% LDPE/LLDPE
28% LDPE/ LLDPE HDPE PVC MEG OTHERS
Fig. 2.1.1: Sectoral usage pattern: Ethylene
2.1.2 Propylene
Propylene is a co-product of ethylene from a cracker complex. It can also be produced by refineries, which set up a propylene recovery unit. The most important end-uses are polypropylene, acrylonitrile, (used to make acrylic fibre,
elastomers like acrylonitrile butadiene rubber: ABR, and speciality polymers like acrylonitrile butadiene styrene: ABS) and cumene, which is further processed into co-products – acetone and phenol. Usage ratio of propylene is given in Table 2.1.2 and sector-wise usage pattern is presented in Fig 2.1.2.
Others 19%
16% 10%
Polypropylene 55%
Acrylonitrile Phenol / Acetone
Polypropylene Others Acrylonitrile Phenol / Acetone
Fig. 2.1.2: Sectoral Usage: Propylene
Table 2.1.2: Propylene: Usage Ratios
Downstream Chemical Propylene required per unit
Polypropylene 1.02 Acrylonitrile 1.10
Phenol / Acetone 0.60
2.1.3 C4 Fractions –Butylenes / Butadienes
C4 fractions are co-produced during manufacture of ethylene and propylene in a cracker complex and during catalytic cracking process in refineries. Butadienes are used mainly for synthetic rubber (styrene butadiene rubber: SBR, poly butadiene rubber: PBR), and engineering plastic (acrylonitrile butadiene styrene:
ABS). Sector-wise usage of Butadiene is presented in Fig 2.1.3.
ABS 8%
SBR 48%
PBR 44%
ABS PBR SBR
. 2.1.3: Sectoral Usage : Butadiene Fig
Usage ratio of Butadiene for the manufacture of various products is presented in Table 2.1.3
Table 2.1.3: Butadiene : Usage Ratio
Product Butadiene required per
unit Styrene Butadiene Rubber 0.52
Poly Butadiene Rubber 0.70
Acrylonitrile Butadiene Styrene 0.20 2.1.4 Benzene
Benzene is a basic aromatic chemical. In India, it is produced from a variety of sources: recovered from pyrolysis gasoline (during naphtha cracking), by reforming of naphtha (in refineries), and in steel plants, as a recovery product from coke oven gas obtained during the carbonisation of coal. Benzene is used as a raw material for several important products. These include caprolactum (used for making nylon filament yarn: NFY) ,linear alkyl benzene: LAB (which is used in detergents), styrene (used in polystyrene and styrene butadiene rubber), phenol (used for laminates), nitro-benzene and chloro-benzenes (dye intermediates), and pesticides (DDT and malathion). Sector-wise usage pattern for benzene is depicted in Fig 2.1.4.
Caprolactum 32%
Downstream Org.
Chemials 26%
Maleic Anhydride 18%
LAB 20%
Pesticides 4%
Caprolactum LAB Pesticides Downstream Org.
Chemicals Maleic Anhydride
Fig.2.1.4: Sectoral Usage pattern: Benzene
Unit wise consumption of Benzene for manufacture of various down stream products is indicated in Table 2.1.4.
Table 2.1.4: Benzene: Usage Ratios
Product Benzene required per unit
Caprolactum 1.00
LAB 0.37 Styrene 0.75 Phenol 1.16 Others 1.33 2.1.5 Toluene:
Toluene is a basic aromatic chemical produced in reformer along with benzene and xylene. It is also produced as a by-product of naphtha cracking. It is mainly used as a solvent in a wide range of end-use sectors. The other major end uses are nitrotoluenes, toluene sulphonamide, dyes, pesticides, chlorinated derivatives and drugs. Sectoral usage of Toluene is presented in Fig. 2.1.5
Pesticides &
Drugs 16%
Chemicals &
Chlorinated deriv.
18%
Nitrotoluene 15%
Others 4%
Solvents &
Thinners
47% Others
Nitrotoluene
Chemicals & Chlorinated deriv.
Pesticides & Drugs Solvents & Thinners
Fig.2.1.5 : Sectoral Usage Pattern : Toluene
2.1.6 Xylene
Commercially important xylenes are of two kinds: paraxylene and orthoxylene.
Para xylene is used for the manufacture of DMT and PTA and this is the backbone of the synthetic fibre industry. Ortho xylene is mainly used in the production of phthalic anhydride (used for manufacture of plasticisers / paints / thinners). Ortho xylene and para xylene are produced in a reformer with naphtha or C5 reformate as inputs.
2.2 Feedstock Choice
A wide range of alternative feed stocks such as naphtha, ethane/propane, alcohol, LPG, NGL and gas oil can be used for production of Petrochemicals. In India, naphtha and C2/C3 fractions from natural gas are the main feedstock used. LPG is normally used as domestic fuel, while gas oil is not used because it is heavier fraction and needs complex processing. In India, some refineries crack LPG in their fluid catalytic cracking units to produce propylene. Summary of various feedstock used by Indian petrochemicals majors is presented in Table 2.2.1
From the table, it is apparent that about 59% of India’s cracking capacity is based on natural gas, whereas 40% is based on Naphtha feedstock. Industrial alcohol which was an attractive feedstock in the days of alcohol price control is no longer an important feedstock and accounts for only 0.8% of the total ethylene production in the country. The major factors, which affect the choice of feedstock, are the relative yields of olefins and aromatics desired, energy costs, investment levels, availability and relative pricing. Natural gas and NGL yield a much higher proportion of ethylene. Hence, they are preferred when the polyolefins output of a cracker is sought to be maximised. On the other hand
naphtha is preferred when a wider range of output products (including propylene and butadiene derivatives) is desired.
Table 2.2.1: Plant-wise feedstock requirement Complex Ethylene
Capacity (TPA)
Feed stocks IPCL, Vadodara 1,30,000 Naphtha
IPCL-MGCC,
Nagothane 4,00,000 Gas (C2/C3 7:3), ethane-propane fraction
Gas (C2/C3 7:3), ethane-propane fraction
IPCL, Gandhar 3,00,000
RIL, Hazira 7,50,000 Naphtha / Natural Gas Liquid
NOCIL, Thane 75,000 Naphtha
HPL, Haldia 4,20,000 Naphtha
GAIL, Auriya 4,00,000 Gas (C2/C3 9:1) Oswal Agro,
Mumbai 22,000 Alcohol
2.3 Downstream Petrochemicals
Downstream Petrochemicals are the products made from basic petrochemicals and thus are derivatives of naphtha or gas. The downstream petrochemicals can be further classified into the Synthetic Organic Chemical Manufacturing Industry (SOCMI) (comprising chemicals/intermediates made from basic petrochemicals) and polymers (such as polyethylene / PVC etc.). The detail of downstream petrochemicals production in India is given below.
2.3.1 Products Based on Ethylene
2.3.1.1 Ethylene Oxide (EO) and Ethylene Glycol (EG)
Ethylene oxide is an intermediate product during the manufacture of mono ethylene glycol (MEG). In India, EO is produced through the Petrochemical and alcohol routes. Ethylene glycol used in the polyester fibre / filament industry (@70%) with minor usage in explosive and anti-freeze coolants.
Installed capacities for ethylene oxide/ethylene glycols are given in Table 2.3.1.1
Table 2.3.1.1:Installed capacities of ethylene oxide/ethylene glycol
Unit Location Capacity (TPA) Feedstock IPCL Vadodara, Gujarat 20,000 Naphtha ethylene NOCIL Thane, Maharashtra 24,000 Naphtha ethylene
RIL Hazira, Gujarat 3,40,000 Naphtha / NGL
ethylene
SM Dyechem Pune, Maharashtra 14,000 Alcohol ethylene
India Glycols 13,000 Alcohol ethylene
IPCL-MGCC Nagothane,
Maharashtra 55,000 Gas ethylene
IPCL Gandhar, Gujarat 1,20,000 Gas ethylene Ethylene oxide finds other uses in surfactants (50%), dye and dye intermediates, amine derivatives and glycol ethers.
2.3.1.2 Ethylene Dichloride/Vinyl Chloride
Ethylene dichloride is an intermediate for vinyl chloride monomer, which polymerises to polyvinyl chloride (PVC). Installed capacities of major units are presented in Table 2.3.1.2
Table 2.3.1.2: Installed capacity of EDC / VCM S.
No. Manufactured Year of
Establishment Technology
Supplier Design Capacity
(TPA) 1 IPCL, Vadodara 1983-84 Stauffer Chemicals,
USA 57,300
2 IPCL, Dahej 1997-98 Innovyl Belgium 1,70,000
3 NOCIL, TTC 1961 Shell, Netherlands 30,000
4 RIL, Hazira 1996 Geon, USA 2,70,000
5 Finolex Pipes
Limited, Ratnagiri 1992/2003 UHDE, Germany 2,40,000 Installed Capacity Data – Basis VCM
2.3.1.3 Ethyl Benzene/Styrene:
Major use of Ethyl Benzene is for production of styrene. Ethyl Benzene is made by alkylation of Benzene in presence of catalyst.
2.3.2 Propylene Based Petrochemicals
2.3.2.1 Propylene Oxide and Propylene Glycol
Propylene Oxide is used for the manufacture of propylene glycol which finds application in Polyester resins, cellophane and food and drug industries.
Propylene oxide is produced by the direct oxidation of propylene.
2.3.2.2 Acrylonitrile (CH2=CHCN)
Acrylonitrile (ACN) is the basic input for the production of acrylic fibre (AF). It is also used to produce acrylonitrile butadiene styrene rubber (ABS) and acrylates.
Acrylonitrile is produced by air oxidation of propylene and ammonia mixture.
IPCL is the sole producer of ACN in India producing about 30,000 TPA at its Vadodara Complex.
2.3.2.3 Isopropyl Alcohol [(CH3)2 . CHOH]
Isopropanol finds its largest use as multipurpose industrial solvent and for manufacture of various drugs and fine chemicals. NOCIL (25,000 TPA), Herdellia in Thane district and IOC in Raigad, Maharashtra manufacture Isopropanol from propylene.
2.3.2.4 Cumene [Isopropyl Benzene - C6H5 . CH . (CH3)2]
Cumene is produced by propylene alkylation of Benzene. Most of the cumene produced is used for captive production of phenol / acetone. HOC - Ernakulum unit extracts propylene from LPG supplied by Cochin refineries limited and uses this for the production of cumene. Its installed capacity is 54,000 TPA. Herdellia chemicals, Thane gets propylene from NOCIL / MRL and uses this for production of cumene. Its installed capacity is 40,000 TPA.
2.3.2.5 Phenol / Acetone
Phenol is used to produce phenol - formaldehyde resins and derivatives such as bisphenol - A, salicylic acid and alkyl phenols. Acetone is used as a solvent, for manufacture of chemicals such as acetone cyanohydrin, di-acetone alcohol, in pesticides, pharmaceuticals, explosives etc. Phenol and acetone are co-produced from air oxidation of cumene and benzene (cumene in turn is produced from propylene). Hence, phenol and acetone economics are closely interlinked.
Acetone is also produced through the alcohol route. The current installed capacity for phenol is about 65,000 TPA. Acetone capacity is about the same, with 50,000 TPA produced as co-product of phenol and remaining through the alcohol route.
2.3.2.6 Butanol and 2-Ethyl Hexanol
An oxo process involves substitution of HCHO across a double bond using a reaction of olefin and CO + H2 synthesis gas. The primary product is an aldehyde (CHO group), which can be hydrogenated to an alcohol. NOCIL employs the oxo process for manufacture of Butanol (normal and iso) and 2 Ethyl hexanol. The total capacity for chemicals manufactured by the process is 20,000 TPA.
2.3.3 Petrochemicals from Benzene 2.3.3.1 Cyclohexane and Caprolactum
Cyclohexane is used as an intermediate for production of caprolactum and as a solvent for manufacture of HDPE. It is produced by hydrogenation of Benzene.
Cyclohexane is produced in the country by GSFC, Gujarat and FACT, Cochin both manufacture caprolactum. Caprolactum is the main input for the production of nylon filament yarn, nylon tyre cord and nylon industrial yarns caprolactum is made from cyclohexanone oxime, which is obtained by treating cyclohexanone with hydroxylamine.
2.3.3.2 Maleic Anhydride (MAN-C4H2O3)
Maleic anhydride (MAN) is used to produce agrochemical, unsaturated polyester resins, alkyd resins and food acids. These in turn are used in a wide range of end use sectors including engineering plastics, helmets, tabletop lamination, pharmaceuticals, varnishes, paints etc. MAN is manufactured by air oxidation of Benzene or n-Butadiene in a process similar to phthalic anhydride. Major producers include Thirumalai Chemicals, Tamilnadu (10,000TPA) and Ganesh Anhydride, Tarapur, Maharashtra (12,000 TPA). Total capacity in 1994-95 was 34,950 TPA, around 75% of MAN output is exported.
2.3.4 Petrochemicals from Toluene 2.3.4.1 Toluene Di Isocyanate (TDI)
TDI is used in the manufacture of polyurethane plastics. It is manufactured by phosgenation of toluene diamine. The sole producer of TDI in the country is Narmada Chemateur India Ltd. Production capacity is 10,000 TPA.
2.3.5 Chemicals from Xylene
2.3.5.1 Terephthalic Acid (PTA) and Dimethyl Terephthalate (DMT)
Purified terephthalic acid (PTA) and dimethyl terephthalate (DMT) are substitute raw materials for production of polyesters (PSF, PFY, PET, polyester films and chips). There are only four manufacturers of DMT / PTA in India. Reliance is the sole producer of PTA at its Patalganga and Hazira plants. Bombay Dyeing (Patalganga), IPCL (Vadodara) and BRPL, Assam produce DMT.
2.3.5.2 Phthalic Anhydride (PAN)
Phthalic anhydride is used to produce unsaturated polyester resins, esters, alkyd resins, specific dyes and pigments. These in turn are used in a wide range of applications of which the most important are the PVC processing industry (esters) and the paint industry (alkyd resins). Ortho xylene is the main raw material of PAN. The installed capacity and production data for phthalic anhydride are presented in Table 2.3.5.2.
Table 2.3.5.2: Capacity / production data of Phthalic Anhydride (PA) Production data
Company Capacity
1996-97 1997-98 1998-99
IGPL, Taloja 1,20,000 80,000 70,000 56,000
MPCL, Karnataka 12,000 12,000 12,000 11,100
TCL, Thirumalai 90,000 35,000 24,000 22,000
Asian Paints, Ankleshwar 25,000 18,000 16,000 13,000
Herdillia, Mumbai 10,000 6,000 5,000 4,500
Ambuja, Andhra Pradesh 9,000 closed closed 2,500 Note: Capacities are as of 1999 – 2000
2.4 Observations and Findings - Industry Survey
This industry survey of the petrochemicals sector brings out the following:
1. Amongst the basic petrochemicals, the olefins (viz. ethylene, propylene and butadiene) are made by cracking of natural gas, C2/C3 fraction of natural gas and naphtha. Currently, 59% of the country’s ethylene capacity is based on gas and 40% on naphtha.
2. Use of alcohol as feedstock for ethylene manufacture is declining fast and many units are facing closure. However, alcohol is used to manufacture number of downstream petrochemicals like aldehydes / ketones.
3. The aromatics (benzene, toluene and xylene) on the other hand are produced by number of processes: recovered from pyrolysis gasoline (during naphtha cracking) as recovery products from coke oven gas and by reforming naphtha. The refineries account for 48 %, whereas crackers account for 42 % of total Benzene production. There have been rapid increases in p-xylene production capacity due to capacity enhancement of synthetic fibres.
4. Natural gas results in higher yields of ethylene compared to other olefins.
Naphtha on the other hand gives a wider range of output products (including propylene, butadiene derivatives).
5. There are no manufacturers of ethyl benzene, styrene monomer and methylene di-isocyanate in the country. Also, 2-ethyl hexanol and butanol is also not been manufactured at NOCIL.
6. It can be observed that the downstream petrochemical industry is widely dispersed, manufacturing wide range of products of varying capacities and employing differing technologies.
Chapter –3
MANUFACTURING PROCESS 3.0 UNIT PROCESS
Cracking and reformation are two main unit operations involved in the manufacturer of Petrochemicals.
(A) Cracking
In cracking a hydrocarbon molecule is fractured or broken into two or more smaller fragments. There are three principal types of cracking:
thermal cracking, catalytically cracking and hydro cracking.
Thermal cracking for fuel production is performed by subjecting a feedstock to temperature usually in excess of 455oC and at above atmospheric pressures with the objective of converting a residual crude fraction or a heavy distillate into gasoline and light distillate.
Catalytic cracking is performed in presence of a catalyst at temperature between 455oC- 540oC and at above atmospheric pressure. The process converts a distillate feedstock in to gasoline as the primary product with production of light hydrocarbons.
Hydro cracking process operates at elevated pressure in the presence of hydrogen and catalyst at temperature generally less than 432oC.
(B) Reforming
The purpose of reforming naphtha is to rearrange or reform the molecular structure of hydrocarbon, particularly with the objective of producing aromatics. The chemical processes involved in reformation are as follows:
¾ Dehydrogenation of naphthenes to aromatics
¾ Dehydrocyclisation of paraffins to form aromatics
¾ Isomerisation of paraffins to more highly branched isomers
As the reaction proceeds the reformed products will contain increasing concentration of aromatics and decreasing concentration of heavy paraffins. These reforming reactions are regulated by metal catalysts in an environment of hydrogen under moderate pressure.
The manufacturing process of important primary and intermediate products, are described below.
3.1 Ethylene/Propylene
Ethylene and propylene are produced by thermal cracking of hydrocarbons. A process flow diagram for a plant producing ethylene from naphtha and or natural gas is shown in Fig. 3.1. Naphtha and/ or natural gas, diluted with steam, is fed in parallel to a number of gas or oil fired tubular pyrolysis furnaces. The fuel for these furnaces is supplied from gas and oil fractions recovered from the cracked gas in later separation stages i.e. ethane and propane. Ethane and propane, which are present in the cracked gas, are separated in later distillation steps, are mixed and recycled through a separate cracking furnace. The flue gas from this pyrolysis furnace is being emitted through furnace stack.
During this operation, coke accumulates on the inside walls of the reactor and each furnace are periodically taken out of service for removal of the accumulated coke. Present day, plants de-coked by on-line i.e. by passing steam and air through the coil while the furnace is maintained at an elevated temperature, effectively burning the carbon out of the coil. While a furnace is being de-coked, the exhaust is diverted to an emission control device (Vent A in Fig. 3.1) whose main function is to reduce particulate emissions.
The cracked gas leaving the pyrolysis furnace is rapidly cooled (oil) to 250 to 300oC and steam is generated. The gaseous streams are then further quenched by the injection of recycled pyrolysis fuel oil from the gasoline fractionators. The quenched cracked gas passes to the gasoline fractionators where pyrolysis fuel oil is separated. Most of the fuel oil is cooled and recycled to the oil quenching operation. The surplus fuel oil passes to the stripper, where light fractions are removed, and then it is send to fuel oil storage. The light fraction removed in the fuel oil stripper is recycled to the gasoline fractionators.
The overhead stream from the gasoline fractionators passes to the water quench tower, where C5’s and heavier compounds are separated. Most of the water separated in the quench tower, is cooled and recycled to the quench tower. Part of the water is passed through dilution steam generators to generate steam and bleed outside as effluent.
On leaving the water quench tower, the pyrolysis gas is compressed to about 3.5 kPa in five stages. Water and organic fractions condensed during compression and cooling are recycled to the quench tower and gasoline stripper, respectively.
Following compression, acid gas (H2S and CO2) is removed by absorption in diethanolamine (DEA) / other similar solvents in the amine wash tower (amine treator) followed by a caustic wash (caustic scrubber). The amine stripper strips the acid gas from the saturated DEA and the DEA is recycled to the amine wash tower. The waste caustic solution & blow down from the DEA cycle are neutralized, stripped of acid gas, and removed as liquid waste streams. The acid
gas stripped from the DEA and caustic waste passes to an emissions control device (Vent C) primarily to control H2S emissions.
After acid gas removal, the remaining process gas stream is further compressed and passed through drying traps containing a desiccant, where the water content is reduced to the low level necessary to prevent ice formation in the low- temperature distillation operations.
With the exception of three catalytic hydrogenation operations, the remaining process involves a series of fractionations in which the various product fractions are successively separated. The de-methaniser separates a mixture of hydrogen and methane from the C2 and heavier components of the process gas. The de- methaniser overhead stream (hydrogen and methane) is further separated into hydrogen rich & methane rich streams in the low temperature chilling section.
The methane rich stream is used primarily for furnace fuel. Hydrogen is required in the catalytic hydrogenation operations.
The de-ethaniser separates the C2 components (ethylene, ethane and acetylene) from the C3, and heavier components. Following catalytic hydrogenation of acetylene to ethylene by the acetylene converter, the ethylene –ethane split is made by the ethylene fractionators. The overhead from the ethylene fractionators is removed as the purified ethylene product, and the ethane fraction is recycled to the ethane /propane cracking furnace.
The de-ethaniser bottoms (C3 and heavier compounds) pass to the de-propanizer where a C3-C4 split is made. The de-propaniser overhead stream (primarily propylene and propane) passes to a catalytic hydrogenation reactor (C3
converter), where traces of propadiene and methyl acetylene are hydrogenated.
Following hydrogenation, the C3 fraction passes to the propylene fractionators, where propylene is removed overhead as a purified product. The propane is recycled to the ethane / propane pyrolysis furnace.
The C4 and heavier components from the de-propaniser pass to the de-butaniser, where a C4 – C5 split is made. The overhead C4 stream is removed & may be treated as follows:
¾ For recovery of butadiene (IPCL Vadodara, HPL Haldia, NOCIL)
¾ Hydrogenation in Catalytic Hydrogenation Unit to form Butane with / without Butadiene extraction (HPL Haldia / RIL, Hazira)
¾ Used as feed into the ethylene process (RIL Hazira)
¾ Use as fuel for furnaces in the ethylene process
The stream containing C5 and heavier component from the debutaniser is combined with the bottoms fraction from the gasoline stripper as raw pyrolysis
gasoline. The combined stream is hydrogenated in the gasoline treatment section. Following the stripping of light fraction, which are recycled to the cracked-gas compressor, the C5 and heavier compounds are transferred to storage as treated pyrolysis gasoline. This stream contains benzene and other aromatics formed by pyrolysis.
3.2 Butadiene
Butadiene are produced by solvent extraction or extractive distillation process wherein the butadiene is extracted by a solvent viz. acetonitrile, cuprous ammonium acetate (CAA), n-methyl pyrolidone (NMP), furfural, dimethyl formamide (DMF) or dimethyl acetamide. No single solvent has dominated the process worldwide and this suggests that there are no significant differences in both operation and economics using most of these solvents. The solvents used in India are Acetonitrile (NOCIL, TTC) and N-Methyl pyrolidone (IPCL, Vadodara
& HPL, Haldia).
A simplified process flow diagram is presented in Fig 3.2.The C4 stream is first taken for feed preparation, where oxygen if any present in it is removed from feedstock by washing with sodium nitrite solution. Washing solution is then distilled to remove C3 hydrocarbons, which are sent back to cracker. The vapour phase mixed C4 hydrocarbons are then contacted and absorbed in the solvent, where butanes & butenes remain largely unabsorbed and are removed as C4
raffinates. The solvent rich in butadiene is distilled to further remove C4
raffinates. The butadiene along with traces of butene, acetylenes & 1-2 butadiene is removed with the solvent. The solvent is then taken to a stripper where the gaseous phase containing butadiene, butane, acetylene etc is stripped off. The gases are then re-extracted with solvent in a second extraction column.
The solvent is then distilled off to remove butadienes, which are then taken further for purification by fractionation. The propynes are separated during butadiene purification. The solvent from stripper & from second-stage extractive distillation column are taken for solvent recovery and then re-used.
The difference in the processing of butadiene lie in the way the solvent is treated for recovery e.g. CAA (Cuprous ammonium acetate) is passed through carbon adsorbers to remove polymers prior to its reuse. Acetonitrile bleed is diluted with water, polymers allowed to separate as oil in coalescer & acetamide/
ammonia removed in a solvent recovery column by distillation. In the NMP process, solvent is regenerated on a continuous basis in vacuum evaporation vessels to remove polymeric solids.
3.3 Ethylene oxide
Ethylene oxide is produced by continuous direct oxidation of ethylene over a silver catalyst. Either air or pure oxygen can be used as the oxidant for the process. The air oxidation process has higher ethylene consumption, higher carbon dioxide production and produces large amounts of off-gas. The oxygen process requires high energy in production of oxygen but allows the recovery of pure CO2 that can be re-used (e.g. for inerting) or sale. However, worldwide there appears to be a trend towards the use of oxygen. In India, all EO plants are based on oxygen and this process is described below.
In the direct ethylene oxidation process, reactions take place in the vapour phase. The two main reactions are:
H2C = CH2 + ½ O2 H2C CH2 (1) Ethylene Oxygen O
Ethylene Oxide
H2C = CH2 + 3O2 2CO2 + 2H2O (2) Ethylene Oxygen Carbon dioxide Water
The formation of 25 to 30 percent of the ethylene to carbon dioxide and water, as given in Reaction (2) is major drawback of the oxidation process. Reaction (2) also releases thirteen times as much heat energy as does Reaction (1). Reaction (2) can be suppressed by replacing the catalyst regularly and by carefully controlling the temperature on the surface of the catalyst, thereby limiting the conversion of ethylene to CO2 and H2O on each catalyst pass to less than 30 percent.
Fig. 3.3 illustrates the basic operations that may be found in the direct oxidation process. The stream and vents shown in Fig. 3.3 are described below. In the Oxygen oxidation process, ethylene and oxygen (streams 1 & 2) enter the reactor. The reaction takes place over a silver catalyst packed in tubes, the heat from the reaction is dissipated by a jacket of heat transfer fluid. Reaction temperature and pressure are maintained at 220o to 280oC and 1 to 3 MPa The activity of the catalyst can be enhanced by the addition of promoters such as alkali metals or alkali earth metals. Catalyst inhibitors such as Ethylene dichloride are added to suppress conversion of ethylene to carbon dioxide while not interfering with the primary reaction. In addition to the main by-product, carbon dioxide, small amounts of acetaldehyde (less than 1%) and traces of formaldehyde are also produced.
Descriptions of Streams And Vents Illustrated In Fig. 3.3
Code Number Description in Fig 3.3 Stream
1 Ethylene feed, >98 mole percent 2 Oxygen feed, >97-99 mole percent
3 Recycle to primary reactor, 0.006 percent EO 4 Primary reactor product gas, 2 percent EO 5 CO2 purge stream
6 CO2-free recycle to primary reactor 7 CO2-rich CO2 absorbent (KHCO3) 8 Reactivated CO2 absorbent (KHCO3) 9 Absorber bottoms, minor EO levels 10 Recycle water to absorbers
11 Reabsorber Vent
12 Recycle Water to Reabsorber
Vent
A CO2 desorber vent (CO2, purge)
B Inert Purge
Effluent
E1 CO2 absorbent
E2 Water stripped during EO purification
The effluent from the reactor (stream 4) contains Ethylene oxide, Ethylene and carbon dioxide. It is cooled, compressed, and passed through the primary absorber. As it passes up the packed column absorber counter current to cold water, the ethylene oxide and some of the carbon dioxide, hydrocarbons and aldehydes dissolve in the water.
Most of the unabsorbed gas that exits the top of the absorber is cooled and becomes the recycle stream (stream 3). A smaller portion of the unabsorbed gas stream (stream 5) is purged to prevent the accumulation of inert gases such as CO2 and Argon (which is present as an impurity in oxygen). The purge gas is passed through a CO2 absorber, which uses potassium carbonate as an absorbent, then (as stream 6) joins the recycle to the reactor. The spent
potassium carbonate (stream 7) is reactivated in the CO2 stripper, then recycled to the CO2 absorber (stream 8). The CO2 is vented from the CO2 stripper (Vent A). A vent stream (Vent B) is taken from the recycle gas in order to reduce the build-up of inerts like ethane, argon & nitrogen, impurities present in the ethylene & oxygen feedstock. The inerts vent is typically used as fuel gas &
burned (e.g. in cracker furnace or stream boiler) & or flared (IPCL, Dahej)
The dilute aqueous solution of EO from the absorber are taken to a stripper, where EO and dissolved inert are distilled under reduced pressure. The stripper water virtually free of EO is re-circulated to the absorbers (stream 10). The crude EO from the desorber is then reabsorbed in water. The EO from the re-absorber is sent for refining/purification. The off-gas from the re-absorber (steam 11) contains large quantity of ethylene and is recycled back to the oxidation stage.
The final product 99.5 mole percent EO is stored under nitrogen pressure.
3.4 Ethylene Glycol
The crude EO from re-absorber/purified EO product is hydrolysed with water in a pipe reactor. The large amount of excess water is removed in a multiple effect evaporator. The water removed from the evaporator (stream 13) is used back in MEG reactor. The Ethylene glycol is then taken to a MEG Column where MEG is separated from higher glycols. The column bottoms (containing higher glycols) are further taken for separation of di-ethylene glycol and tri-ethylene glycol column residues are sold as heavier glycols/polyethylene glycols. Fig 3.4 presents the block flow diagram of Ethylene glycol manufacture and present.
Stream descriptions of vents and stream in Fig 3.4 is given below:
Code Number Description in fig 3.4 Stream
13 Recycle water to MEG Reactor 14 MEG with trace moisture
Higher glycols streams (containing DEG/TEG/Polymeric glycols)
15 Effluent
E3 Water removed during evaporation & drying of EO E4 Water from vacuum system (MEG/DEG)
Various chemical reactions taking place during EO/EG manufacture are listed below:
Product Reactions
1. C2H4 + ½ O2 C2H4O Ethylene Oxygen Ethylene oxide
